Functionalization of monofluoroallene and the synthesis of aryl-substituted conjugated fluorodienes

[reaction: see text] 4-Fluoroallenol 3a, prepared from 1, cyclized easily to 4 but preserved its fluoroallenyl integrity under oxidation and S(N)2 displacement to yield aldehyde, amine, mesylate, and halide 6. Allylic isomerization yielded 2-halo-1-fluoro-1,3-butadiene 7, which underwent a Suzuki coupling to give aryl-substituted conjugated diene 8.     

Regiospecific synthesis of bicyclo- and heterobicyclo-gem-difluorocyclobutenes using functionalized fluoroallenes and a novel Mo-catalyzed intramolecular [2 + 2] cycloaddition reaction

The first synthesis of functionalized gem-difluoroallenes 4 served as platform for an unprecedented molybdenum-catalyzed intramolecular allene-alkyne [2 + 2]-cycloaddition that produced 6, a hitherto unknown class of bicyclo- and heterobicyclo-CF2-containing cyclobutenes.     

In-beam spectroscopy of 253, 254No

In-beam conversion electron spectroscopy experiments have been performed on the transfermium nuclei ^{253, 254}No using the conversion electron spectrometer SACRED in nearly collinear geometry in conjunction with the gas-filled separator RITU at the University of Jyv?skyl?. The experimental setup is discussed and the spectra are compared to Monte Carlo simulations. The implications for the ground-state configuration of ²⁵³No are discussed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rdh@ns.ph.liv.ac.uk RID="b" ID="b"Present address: GANIL, F-14021 Caen, France. RID="c" ID="c"Permanent address: IReS Strasbourg, IN2P3-CNRS, F-67037-Strasbourg, France. RID="d" ID="d"Present address: CEA/DIF DCRE/SDE/LDN F-91680 Bruyeres-le-Chatel. RID="e" ID="e"Present address: Daresbury Laboratory, Daresbury WA4 4AD, UK. RID="f" ID="f"Permanent address: IPN Lyon, IN2P3-CNRS, F-69037 Lyon, France.     

QUENCHING OF A RETINAL TRIPLET STATE BY A NITROXYL RADICAL

Abstract— The long lived triplets from all-trans retinal and 11-cis retinal are quenched by a nitroxyl radical, 4-hydroxy-2,2,6,6-tetramethylpiperidinoyl, with essentially identical rate constants. The rates vary with solvent but do not correlate with solvent polarity. The results confirm implications of earlier work with oxygen quenching and are compatible with the view that isomerization occurs in non-relaxed triplets or that the triplet (or triplets) observed spectroscopically decay by way of a single triplet state which has a small electronic energy gap to ground state isomers.     

On the non-existence of perfect and nearly perfect codes

The main result of the paper is the proof of the non-existence of a class of completely regular codes in certain distance-regular graphs. Corollaries of this result establish the non-existence of perfect and nearly perfect codes in the infinite families of distance-regular graphs J(2b + 1, b) and J(2b+2,b).     

Electron hole condensate radiation from Ge double injection devices between 1.5° and 4.2°

Carrier injection in Ge at helium temperatures produces radiation characteristic of the electron hole condensate. Time resolved spectra are used to analyze the presence of both condensate and free exciton radiation at high power levels. Device heating is indicated.     

Observation of triplet doubly excited states in single photon excitation from ground state helium

We have observed, for the first time, LS-forbidden triplet doubly excited states, in single photon excitation of ground state helium, below the second ionization threshold. These states are identified as (3)D(o) and (3)P(o) and their excitation is due to spin-orbit interaction that mixes them with the optically allowed (1)P(o) states. This observation is possible due to the very high efficiency in detecting metastable atoms created after the fluorescence decay of the doubly excited states, and the new capabilities of third generation synchrotron vacuum ultraviolet sources with high resolution beam lines.     

Radiative decay of doubly excited states in helium below the He+ (N = 2) ionization threshold

The radiative decay of (1)P(o) doubly excited states in helium has been investigated using a novel apparatus in which metastable atoms and vacuum ultraviolet photons are detected. The intensity ratio of the energetically narrow (sp,2n-)(1)P(o) and (2p,nd)(1)P(o) series to the broader (sp,2n+)(1)P(o) series is strikingly enhanced in comparison with conventional photoabsorption, photoion, or photoelectron measurements using synchrotron radiation. The experimental approach is a new way forward for the study of energetically narrow doubly excited states.